When charge is at rest then it creates only electric field not the magnetic field. A moving charge generates electric as well as magnetic field around it. If charge is moving with constant velocity then electric and magnetic field do not change with time, hence, it cannot produce electromagnetic wave. When charge is accelerated then time-varying electric and magnetic fields are created and thus electromagnetic wave is produced by accelerated charge. We know that the current-carrying wire creates magnetic field around it. If alternating current is flowing through the wire then it creates variable magnetic field around it and thus starts radiating electromagnetic waves. When a charged capacitor is connected across an inductor then charge starts oscillating between the plates of the capacitor. Normally one plate of the capacitor is connected to Earth and the other plate is connected to an antenna. Antenna radiates electromagnetic wave. Hertz successfully produced electromagnetic waves using such LC oscillator. Speed of electromagnetic wave in vacuum is constant and equal to `3 xx 10^8` m/s. But inside a medium the speed changes according to electrical and magnetic properties of the medium.
Which of the following cannot create electromagnetic wave ?

Options

A. Wire carrying alternating current
B. Oscillating charge
C. Wire connected to a DC power source
D. charge moving in a circular path

Answer

C

Explanation

Wire connected to a DC power source will carry constant current through it and hence cannot create time - varying magnetic waves .in all other cases electromangnetic waves are producted . Hence option ( c) is correct .